Selective Catalytic Reduction (SCR) systems may be included in an exhaust treatment or aftertreatment system for a power system to remove or reduce nitrous oxide (NOx or NO) emissions coming from the exhaust of an engine. The SCR systems include a catalyst and the introduction of a reductant to the exhaust stream upstream of the catalyst. A common reductant used is urea, which is broken down into a redutent product such as ammonia (NH3) that is adsorbed or stored in (or on) the catalyst. The reductant and reductant product may be commonly referred to as the “reductant.” The ammonia product reacts with NOx in the exhaust to convert the NOx to Nitrogen (N2) and water (H2O).
Controllers monitor engine and aftertreatment component parameters to determine the amount of reductant to be added. However, situations may arise where excess reductant is introduced and not all the reductant is stored, resulting in reductant “slip.” Reductant “slip” involves the redcuant exiting the SCR and being released to the environment.
U.S. Patent Publication No. 2008/0202097 (the '097 publn) describes a system for introducing reductant to an exhaust stream. The '097 publn discloses the monitoring of SCR temperature and the use of a controller to control the injection of reductant.